Unlike other display options, this one was missing a description.
This clarifies the option's purpose and the fact that it displays
the host's CPU usage, not the emulated system's CPU usage.
- Use CMake's `-B` option to automatically create the build folder
and avoid the `cd` requirement.
- Use CMake's build tool-agnostic `--build` option to use the same
build command regardless of whether GNU Make or Ninja is used.
`--parallel` also ensures that all CPU threads are used by default.
- Mention optional dependency on Ninja for macOS (it's confirmed to work
there, installed from Homebrew).
- Update Qt macOS path to use the default installation path on a modern
Homebrew installation. The old path is still mentioned just in case.
- Mention that the generated macOS application bundle may have to be
manually resigned before it can be run.
The macOS build steps were successfully followed on a 2020 Mac mini
(Apple M1).
Hugo Locurcio